This study is the third stage of the project initiated on April 1, 1979. It deals with the problem of genome reorganization during animal development. We have chosen the model system Tetrahymena for this investigation. Two specific problems are currently being examined: amplification of ribosomal RNA gene and elimination of some specific sequences. Using recombinant DNA techniques we have isolated some of the DNA fragments involved in these processes from the germinal micronucleus. In this study period we are trying to determine the nucleotide sequences in the relevant regions of these cloned DNA, such as the junction between rDNA and the flanking region. We are also examining the changes that occur to these regions of the genome during development. Effects of environmental factors such as temperature and nutrients on these alteration processes will also be investigated. It is hoped that this study will lead to a better understanding of the stability and the differentiation of eukaryotic genomes.